Aircraft jet engine cooling system



March l17,v 1953 A. WILLIAMSON, JR., ET A1. 2,631,796

AIRCRAFT JET ENGINE COOLING SYSTEM Filed July 24, 1950 F.' 2 P05/mf@.24am/vr r @655025 A @wap ja, 40) 17a,

.Patented Mar. 17,1953 Y UNITED STATES PATENT QFFICE 2,631,796 AIRCRAFTJET ENGINE. COOLING. SYSTEM Application July 24, 1950,y Serial No.175,538

Claims.

l The present invention relates to jet engine cooling systems, and, moreparticularly, to such a cooling system for use when the jet engine isinstalled in high speed aircraft.

It is customary, when jet engines are installed in aircraft, toterminate the jet tail pipe just lshort of an engine encircling shroudspaced from the engine casing; this arrangement causes a negativepressure to be created at the exhaust end of the installation. Air iscustomarily admitted between the shroud and the engine ahead of thecombustion chambers, turbine and tail pipe of the engine through anairscoop. During iiight, a ram pressure is developed in the airscoopwhich, combined with the negative pressure at the exhaust end of theengine, causes a satisfactory cooling ilow of air to pass through theshroud. On the ground, however, and at low airplane speeds, ram pressureis absent or very small, and the cooling flow is substantially entirelydependent upon the negative pressure developed by the ejector action ofthe jet.

On very high speed airplanes, the drag of special engine coolingairscoops is undesirable, and it is advantageous to inlet the enginecooling air through the jet engine inlet and duct, thereby completelyeliminating the special cooling airsccop. The action of such a coolingair inlet is satisfactory as long as positive ram pressure is obtainedin the jet inlet, such as will exist when the aircraft is in iiight, butis not satisfactory when the engine is running on the ground or at lowaircraft speeds. This isbecause the suction developed by the compressorof the jet engine causes a negative pressure to be created in the jetengine inlet duct and at the inlet to this duct. When, then, one end ofthe space between shroud and engine is connected tothe jet engine inlet,with the other end connected to the ejector structure at the exhaust endof the jet engine, negative pressures will exist at both places in theabsence of ram, and very little, if any, cooling air flow will result.

It is an object of the present invention to provide a means and methodof obtaining a satisfactory cooling air flow around a jet engine whenthe inlet for the cooling air fiow is common with4 the inlet to the jetengine.

In brief, the present invention includes a shroud around the rearportions of a jet engine as installed in an aircraft. The aft end of theshroud is positioned so that a negative pressure is developed betweenengine and the shroud due to ejector action of the jet exhaust. Theinlet to the shroud is in the main air inlet-to the com- 2 presser ofthe jet engine in a position where the pressure is also negative whenthe airplane is l'stationary or operating at low speeds, such as whentaxiing orv during take-01T. In order that a satisfactoryv coolingcirculation be maintained under these conditions, an auxiliary air inletis provided opening into the shroud between the two negative pressureareas, this latter inlet opening into the atmosphere at an area wherethere is zero pressure when the aircraft is stationary and negativepressure when the airplane is in night. The auxiliary opening isprovided with a flap valve opening inwardly. Under these circumstances,cooling air can enter the auxiliary air inlet freely to flow through theshroud from front to rear and Ventilating air can W from the auxiliaryair inlet around the forward engine sections to the compressor inletwhen the aircraft is stationary. The ap valve automatically closes asram pressure develops in flight and the external pressure at theauxiliary inlet reduces, to establish a straight through, one-waycooling ow in the shroud from the main air inlet.

Other advantages and objects of the invention will be more fullyunderstood by reference to the drawings in which:

Figure 1 is a perspective View of a jet propelled airplane embodying onepreferred form of the present invention.

Figures 2 and 3 are schematized sections taken as indicated by the line2-2 inFigure 1; Figure 2 showing cooling air flow conditions in ight;Figure 3 showing cooling air conditions with the aircraft stationary.

Figure 4; is an enlarged sectional diagram of a flap valve used in thecooling system shown in Figures l and 2.

Referring first to` Figure 1, a high speed jet airplane, such as theUnited States Air Force X-4 airplane, capable of speeds approaching MachNo. 1.0 is provided with a fuselage I, sweptback wings 2, and a pairoi'Y jet engines of the gaseous combustion turbine type disposed in-fairings 3 on each side of fuselage I.

diagrammatically in Figures 2 and 3.

Here, a short inlet duct lll-connects the main air inlet opening withthe front end II of a jet engine I2, the air supply for the jet enginepassing into a compressor section I4 of the engine I2 through the frontend Il. However, front end II is spaced from the aft end of inlet duct Iby spacers I5 to provide an annular cooling air inlet I6 through whichair can pass into a space il between the airplane structure and engineI2. A shroud I8, cantilevered from a mounting flange I9 on the enginecasing, extends rearwardly from the beginning of the combustion andturbine section 2I of the engine I2 and around tail pipe 22 of theengine to terminate at shroud opening 5 beyond the end of tail pipe 22,forming a cooling space Ila between the shroud I8 and engine. A shroudinlet duct Ilia, having a fire screen 20 (Figure 4) in the-front andrear sides thereof, provides an air entrance at the front of the shroudI8. As the jet of hot gases issuing from exhaust opening 24 of the tailpipe 22 passes through the shroud opening 6, a negative pressure will bedeveloped by ejector action tending to draw air through spaces II andIla, by way of the nre screen 2K3. However, as stated above, when theairplane is stationary with the engine running, a negative pressure willalso be present in inlet duct Il! so that little or no cooling flow willresult.

In order that atmospheric air can beadmitted under these conditions, anauxiliary air inlet 353 is provided into the shroud inlet duct ia, thisauxiliary inlet 3Q extending into shroud space Ila from the enginefairing '5 forming a portion of the external surface of the airplane.

As best shown in Figure 4, auxiliary air inletv B is provided with aflap valve SBI, opening inwardly, preferably of impregnated clothsufiiciently flexible to open freely while conforming to the curve ofthe air frame. Flap valve SI is attached to an external flush plate 32having openings 33. Inlets ISa and 3! are disposed annularly around theshroud periphery for a substantially greater distance than thelongitudinal dimension of auxiliary inlet 3d.

The pressure conditions in flight, of the system just described, areshown diagrammatically in Figure 2.

Under these night conditions a positive ram pressure exists in the inletduct I3 at the annular opening I6 into space I'l, and a negativepressure will exist in the annular space between shroud I8 and jet pipe22 at the end of the jet pipe 22. Consequently, an adequate cooling flowwill exist through the entire shroud space ila, coming through the nrescreen 26. As the internal pressure in shroud inlet duct Ida will bepositive, and as there will be a negative pressure just outside of theairplane skin at the auxiliary air inlet 3i],'the flap 3i will close theauxiliary air inlet 313.V A firewall Sli, blocking the space etween theshroud i8 and the engine compartment, performs its usual function andalso insures that substantially full air flow from the inlet duct I9over the entire engine will take place throughout the spaces I'I andIla..

The pressure conditions on the ground with engine operating are shown inFigure 3. In this case, the pressure in inlet duct I0, in the absence ofram, becomes negative, with the pressure at the tail pipe end of theshroud remaining negative. Under these conditions, the pressure inshroud space I'a is negative throughout. With zero pressure at theauxiliary inlet Si), the nap SI will open and cooling air will enterthrough the auxiliary inlet 3B to flowforwardly to the' 4 air inlet ductI0, and rearwardly through shroud space I'Ia to the ejector end of theengine. Ample cooling flow is thus provided when the airplane isstationary. As this ample flow continues as the airplane increases speedto where the air inlet duct I0 pressure changes to positive due to rameffect, and as full front to rear now starts at that speed, amplecooling of the engine is provided under all conditions. Since negativepressures normally exist over the entire midportion of a high speedairplane in flight, proper location of the auxiliary air inlet Se is notonly easy to determine, but is almost unavoidable.

In the X-4 airplane, shown in Figure l, it was found that cooling, usingthe system described herein, was sufficiently good when the engine wasoperating with the airplane stationary or at low speeds, that the normalcomplicated heat insulating blanket over the combustion chambers,turbine and tail pipe could be dispensed with, only a single radiantheat shield 35, such as a polished stainless steel sheet, being requiredbetween shroud I8 and the engine casing, this shield 35 being spacedfrom both shroud and casing so that cooling air can flow 4on each sidethereof. Shield 35 may, for example, be supported from shroud I8 bymeans of longitudinal support members 36 permitting air flow therealong.

A distributing bafe 3S inside of the shroud i8 just aft of the shroudinlet Ia is preferably provided to obtain a uniform air flow on allsides of the engine at the shroud inlet. In the particularembodimentillustrated, a few small ventilating openings 4d are alsoprovided in the engine compartment just forward of the firewall 34, toventilate the `region aft of they shroud inlet Ilia. These openings illar-e of no significance as far as engine cooling is concerned, and theyare too small and few in number to destroy the pressure differentialwhich causes opening of the ap valve SI. For other, more general,ernbodiments, the firewall 35 could be relocated at a more normalposition between the compressor section Ill and the combustion section 2I, and the Ventilating openings 4Q then eliminated.

Also, any satisfactory air inlet from the main inlet duct I0 to thecompressor section space IT could be substituted for the rather unusualslotted design shown herein, and a hinged metal door might be used forthe flap valve 3i and plate 32, provided that the skin curvature wouldpermit same. Other arrangements of this inven tion will readily suggestthemselves to those skilled in the art.

From the above description it will be apparent that there is thusprovided a device of the char acter described possessing the particularfeatures of advantage before enumerated as desirable, but whichobviously is susceptible of modieation in its form, proportions, detailconstruc 'tion and. arrangement of parts without departing from theprinciple involved or sacricing any of its advantages.

While in order to comply with the statute, the invention has beendescribed in language more or less specic as to structural, features, itis to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein disclosedcomprise a preferred form of putting the invention ,into effect, and theinvention is, therefore,

claimed in any of its forms or'mcdications within the legitimate andvalid scope of the appended claims. y i

What is claimed is:

1. In an airplane having a gas turbine engine including compressor,combustion, turbine, and tail pipe sections in that order, and acompressor air inlet duct; engine cooling means comprising a shroudspaced from and positioned around said combustion, turbine and tail pipesections of said engine, said shroud extending aft beyond the end ofsaid tail pipe section to form a negative pressure space between saidshroud and said tail pipe when said engine is running, said shroud beingsealed at its forward end to said engine except for a shroud opening, acooling air inlet duct connected to said shroud opening, said coolingair inlet duct having a second opening flush with the outer surface ofsaid airplane at an area where there is zero pressure when said airplaneis stationary and negative pressure when said airplane is in flight, anda third opening in communication with said compressor air inlet duct,and means opening and closing said second opening in accordance with theresultant of the pressure in said compressor air inlet duct, thepressure in said negative pressure space and the pressure at said secondopening of said cooling air inlet duct.

2. Apparatus in accordance with claim 1 wherein the last mentioned meansis a freely swinging flap valve opening inwardly at said flush openinginto said cooling air inlet duct and controlled as to position by therelative pressure on each side thereof.

3. In an airplane having a gas turbine engine including an air inletopening and a jet exhaust opening, an air inlet duct connected to saidengine air inlet opening and having ram pressure therein only when saidairplane is in flight and a negative pressure therein when said engineis running in the absence of ram, a cooling shroud spaced from andsurrounding at least a portion of the rear of said engine to form anengine cooling space, said shroud extending rearwardly beyond said jetexhaust opening to form a negative pressure space in said shroudadjacent said latter opening, having a negative pressure therein whensaid engine is running, means connecting said shroud with said engineair inlet duct, a cooling air inlet duct having an inward opening intosaid shroud and an outward opening on the exterior surface of saidairplane at an area where there is zero pressure when said airplane isstationary and negative pressure when said airplane is in flight, andclosure means for said outward opening operated by the resultant of thepressures of said engine air inlet duct, said negative pressure spaceand the pressure at the surface area of said airplane at the outer endof said cooling air inlet duct whereby air is drawn through said shroudfrom said area on the exterior surface of said airplane when saidairplane is stationary with the engine running, and from said air inletduct only after ram pressure has developed therein.

4. Apparatus in accordance with claim 3 wherein said cooling air inletduct closure means is a freely swinging nap valve opening inwardly intosaid cooling air inlet duct at said outward opening of said cooling airinlet duct.

5. In an airplane driven by a gas turbine engine, a ram air ductconnected with the forward end of said engine having a negative pressuretherein when said engine is running in the absence of ram and a positivepressure therein due to ram when said airplane is in night, an ejectorduct at the aft end of said engine having a negative pressure thereinwhen said engine is running, a cooling air shroud spaced from` andsurrounding at least a portion of said engine, said shroud beingforwardly connected to said ram air duct and rearwardly to said ejectorduct, and means admitting cooling air at substantially zero pressure tosaid shroud when both said forward and rear connections of said shroudare at a negative pressure.

LOYAL A. WILLIAMSON, J R. GEORGE H. SCHWAB, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,501,633 Price Mar. 21, 19502,508,288 Owner May 16, 1950 FOREIGN PATENTS Number Country Date 579,657Great Britain Aug. 12. 1946

